The objective of this proposed research is to investigate the maternal cardiovascular adjustments which occur during the course of pregnancy. Particular emphasis will be placed on the vasodilation which apparently occurs in some nonreproductive tissues. This research seeks to quantitatively define the role of the steroid hormones, the estrogens and progesterone, in the generation of the increased cardiac output and blood volume, and decreased vascular resistance of pregnancy. Specifically, the forementioned cardiovascular parameters as well as individual organ or tissue blood flows will be measured several times during pregnancy in guinea pigs. In ovariectomized female pigs 17 beta-estradiol and progesterone will be exogenously administered both singly and together on a chronic basis and at physiological doses and their net effect on the cardiovascular system will be again determined as with the pregnant animals. These experiments have not been done in any one species and will help provide a better understanding of the physiology of pregnancy and the effects of steroid hormones on the cardiovascular system.